2,845 research outputs found
Effective Capacity in Wireless Networks: A Comprehensive Survey
Low latency applications, such as multimedia communications, autonomous
vehicles, and Tactile Internet are the emerging applications for
next-generation wireless networks, such as 5th generation (5G) mobile networks.
Existing physical-layer channel models, however, do not explicitly consider
quality-of-service (QoS) aware related parameters under specific delay
constraints. To investigate the performance of low-latency applications in
future networks, a new mathematical framework is needed. Effective capacity
(EC), which is a link-layer channel model with QoS-awareness, can be used to
investigate the performance of wireless networks under certain statistical
delay constraints. In this paper, we provide a comprehensive survey on existing
works, that use the EC model in various wireless networks. We summarize the
work related to EC for different networks such as cognitive radio networks
(CRNs), cellular networks, relay networks, adhoc networks, and mesh networks.
We explore five case studies encompassing EC operation with different design
and architectural requirements. We survey various delay-sensitive applications
such as voice and video with their EC analysis under certain delay constraints.
We finally present the future research directions with open issues covering EC
maximization
Prescient Precoding in Heterogeneous DSA Networks with Both Underlay and Interweave MIMO Cognitive Radios
This work examines a novel heterogeneous dynamic spectrum access network
where the primary users (PUs) coexist with both underlay and interweave
cognitive radios (ICRs); all terminals being potentially equipped with multiple
antennas. Underlay cognitive transmitters (UCTs) are allowed to transmit
concurrently with PUs subject to interference constraints, while the ICRs
employ spectrum sensing and are permitted to access the shared spectrum only
when both PUs and UCTs are absent. We investigate the design of MIMO precoding
algorithms for the UCT that increase the detection probability at the ICRs,
while simultaneously meeting a desired Quality-of-Service target to the
underlay cognitive receivers (UCRs) and constraining interference leaked to
PUs. The objective of such a proactive approach, referred to as prescient
precoding, is to minimize the probability of interference from ICRs to the UCRs
and primary receivers due to imperfect spectrum sensing. We begin with downlink
prescient precoding algorithms for multiple single-antenna UCRs and
multi-antenna PUs/ICRs. We then present prescient block-diagonalization
algorithms for the MIMO underlay downlink where spatial multiplexing is
performed for a plurality of multi-antenna UCRs. Numerical experiments
demonstrate that prescient precoding by UCTs provides a pronounced performance
gain compared to conventional underlay precoding strategies.Comment: 23 pages; Submitted to IEEE Trans. Wireless Commu
MIMO Precoding in Underlay Cognitive Radio Systems with Completely Unknown Primary CSI
This paper studies a novel underlay MIMO cognitive radio (CR) system, where
the instantaneous or statistical channel state information (CSI) of the
interfering channels to the primary receivers (PRs) is completely unknown to
the CR. For the single underlay receiver scenario, we assume a minimum
information rate must be guaranteed on the CR main channel whose CSI is known
at the CR transmitter. We first show that low-rank CR interference is
preferable for improving the throughput of the PRs compared with spreading less
power over more transmit dimensions. Based on this observation, we then propose
a rank minimization CR transmission strategy assuming a minimum information
rate must be guaranteed on the CR main channel. We propose a simple solution
referred to as frugal waterfilling (FWF) that uses the least amount of power
required to achieve the rate constraint with a minimum-rank transmit covariance
matrix. We also present two heuristic approaches that have been used in prior
work to transform rank minimization problems into convex optimization problems.
The proposed schemes are then generalized to an underlay MIMO CR downlink
network with multiple receivers. Finally, a theoretical analysis of the
interference temperature and leakage rate outage probabilities at the PR is
presented for Rayleigh fading channels.We demonstrate that the direct FWF
solution leads to higher PR throughput even though it has higher interference
"temperature (IT) compared with the heuristic methods and classic waterfilling,
which calls into question the use of IT as a metric for CR interference.Comment: 11 page
On Green Multicasting over Cognitive Radio Fading Channels
In this paper, an underlay cognitive radio (CR) multicast network, consisting
of a cognitive base station (CBS) and multiple multicast groups of secondary
users (SUs), is considered. All SUs, belonging to a particular multicast group,
are served by the CBS using a common primary user (PU) channel. The goal is to
maximize the energy efficiency (EE) of the system, through dynamic adaptation
of target rate and transmit power for each multicast group, under the PUs'
individual interference constraints. The optimization problem formulated for
this is proved to be non quasi-concave with respect to the joint variation of
the CBS's transmit power and target rate. An efficient iterative algorithm for
EE maximization is proposed along with its complexity analysis. Simulation
results illustrate the performance gain of our proposed scheme.Comment: 5 pages, 4 figures, Submitted in IEEE Transactions on Vehicular
Technolog
Queueing Analysis for Preemptive Transmission in Underlay Cognitive Radio Networks
In many cognitive radio applications, there are multiple types of message
queues. Existing queueing analysis works in underlay CR networks failed to
discuss packets heterogeneity. Therefore high priority packets with impatient
waiting time that have preemptive transmission opportunities over low class are
investigated. We model the system behavior as a M/M/1+GI queue which is
represented by a two dimensional state transition graph. The reneging
probability of high priority packets and the average waiting time in two-class
priority queues is analyzed. Simulation results demonstrate that the average
waiting time of high priority packets decreases with the growing interference
power threshold and the average waiting time of the low priority packet is
proportional to the arrival rate of the high priority packet. This work may lay
the foundation to design efficient MAC protocols and optimize long term system
performance by carefully choosing system parameters
Spectrum Sharing for Device-to-Device Communication in Cellular Networks
This paper addresses two fundamental and interrelated issues in
device-to-device (D2D) enhanced cellular networks. The first issue is how D2D
users should access spectrum, and we consider two choices: overlay (orthogonal
spectrum between D2D and cellular UEs) and underlay (non-orthogonal). The
second issue is how D2D users should choose between communicating directly or
via the base station, a choice that depends on distance between the potential
D2D transmitter and receiver. We propose a tractable hybrid network model where
the positions of mobiles are modeled by random spatial Poisson point process,
with which we present a general analytical approach that allows a unified
performance evaluation for these questions. Then, we derive analytical rate
expressions and apply them to optimize the two D2D spectrum sharing scenarios
under a weighted proportional fair utility function. We find that as the
proportion of potential D2D mobiles increases, the optimal spectrum partition
in the overlay is almost invariant (when D2D mode selection threshold is large)
while the optimal spectrum access factor in the underlay decreases. Further,
from a coverage perspective, we reveal a tradeoff between the spectrum access
factor and the D2D mode selection threshold in the underlay: as more D2D links
are allowed (due to a more relaxed mode selection threshold), the network
should actually make less spectrum available to them to limit their
interference.Comment: 14 pages; 11 figures; submitted to IEEE Transactions on Wireless
Communication
A Practical Spectrum Sharing Scheme for Cognitive Radio Networks: Design and Experiments
Spectrum shortage is a fundamental problem in wireless networks and this
problem becomes increasingly acute with the rapid proliferation of wireless
devices. To address this problem, spectrum sharing in the context of cognitive
radio networks (CRNs) has been considered a promising solution. In this paper,
we propose a practical spectrum sharing scheme for a small CRN that comprises a
pair of primary users and a pair of secondary users by leveraging the
multiple-input and multiple-output (MIMO) technology. In our scheme, we assume
that the secondary users take full responsibility for cross-network
interference cancellation (IC). We also assume that the secondary users have no
knowledge about the primary network, including its signal waveform, frame
structure, and network protocol. The key components of our proposed scheme are
two MIMO-based interference management techniques: blind beamforming (BBF) and
blind interference cancellation (BIC). We have built a prototype of our scheme
on a wireless testbed and demonstrated that the prototyped secondary network
can coexist with commercial Wi-Fi devices (primary users). Experimental results
further show that, for a secondary device with two or three antennas, BBF and
BIC achieve an average of 25dB and 33dB IC capability in an office environment,
respectively
Techniques for Cooperative Cognitive Radio Networks
The frequency spectrum is an essential resource for wireless communication.
Special sections of the spectrum are used for military purposes, governments
sell some frequency bands to broadcasting and mobile communications companies
for commercial use, others such as ISM (Industrial, Science and Medical) bands
are available for the public free of charge. As the spectrum becomes
overcrowded, there seem to be two possible solutions: pushing the frequency
limits higher to frequencies of 60 GHz and above, or reaggregating the densely
used licensed frequency bands. The new Cognitive Radio (CR) approach comes with
the feasible solution to spectrum scarcity. Secondary utilization of a licensed
spectrum band can enhance the spectrum usage and introduce a reliable solution
to its dearth. In such a cognitive radio network, secondary users can access
the spectrum under the constraint that a minimum quality of service is
guaranteed for the licensed primary users. In this thesis, we focus on spectrum
sharing techniques in cognitive radio network where there is a number of
secondary users sharing unoccupied spectrum holes. More specifically, we
introduce two collaborative cognitive radio networks in which the secondary
user cooperate with the primary user to deliver the data of the primary user.Comment: Master's thesi
A Survey on Device-to-Device Communication in Cellular Networks
Device-to-Device (D2D) communication was initially proposed in cellular
networks as a new paradigm to enhance network performance. The emergence of new
applications such as content distribution and location-aware advertisement
introduced new use-cases for D2D communications in cellular networks. The
initial studies showed that D2D communication has advantages such as increased
spectral efficiency and reduced communication delay. However, this
communication mode introduces complications in terms of interference control
overhead and protocols that are still open research problems. The feasibility
of D2D communications in LTE-A is being studied by academia, industry, and the
standardization bodies. To date, there are more than 100 papers available on
D2D communications in cellular networks and, there is no survey on this field.
In this article, we provide a taxonomy based on the D2D communicating spectrum
and review the available literature extensively under the proposed taxonomy.
Moreover, we provide new insights to the over-explored and under-explored areas
which lead us to identify open research problems of D2D communication in
cellular networks.Comment: 18 pages; 8 figures; Accepted for publication in IEEE Communications
Surveys and Tutorial
Sequential Joint Spectrum Sensing and Channel Estimation for Dynamic Spectrum Access
Dynamic spectrum access under channel uncertainties is considered. With the
goal of maximizing the secondary user (SU) throughput subject to constraints on
the primary user (PU) outage probability we formulate a joint problem of
spectrum sensing and channel state estimation. The problem is cast into a
sequential framework since sensing time minimization is crucial for throughput
maximization. In the optimum solution, the sensing decision rule is coupled
with the channel estimator, making the separate treatment of the sensing and
channel estimation strictly suboptimal. Using such a joint structure for
spectrum sensing and channel estimation we propose a distributed (cooperative)
dynamic spectrum access scheme under statistical channel state information
(CSI). In the proposed scheme, the SUs report their sufficient statistics to a
fusion center (FC) via level-triggered sampling, a nonuniform sampling
technique that is known to be bandwidth-and-energy efficient. Then, the FC
makes a sequential spectrum sensing decision using local statistics and channel
estimates, and selects the SU with the best transmission opportunity. The
selected SU, using the sensing decision and its channel estimates, computes the
transmit power and starts data transmission. Simulation results demonstrate
that the proposed scheme significantly outperforms its conventional
counterparts, under the same PU outage constraints, in terms of the achievable
SU throughput
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